The present invention relates generally to well head equipment for production wells. In particular, this invention relates to tools and methods for sealing the casing-by-casing annulus at the top of the well bore so that a positive pressure may be applied to the annulus.
Production wells typically have a surface casing that extends from the top of the well and into the earth to a relatively shallow depth. It is also typical for a production casing to be positioned concentrically within the surface casing and so as to extend from the top of the well to a relatively deep depth. A casing-by-casing annulus is defined between the surface casing and the production casing.
In certain instances, it is desirable to apply a pressure differential in the annulus relative to atmospheric pressure at the well head. For example, if a reverse circulation cement (RCC) job is to be performed in the annulus, the cement is pumped into the annulus under positive pressure to pump the cement composition down the annulus. Prior to applying the pressure differential in the annulus, steps must be taken to isolate or seal the annulus at the well head. Previously, blow out preventor (BOP) and/or well head equipment has been used to seal the annulus. However, typical blow out preventor and well head equipment do not provide access to the annulus for performing a reverse circulation cement job. Typical blow out preventor and well head equipment limits the use of reverse circulation cementing operations on wells where surface casing is not fitted to accept the wellhead equipment. Further, even where the surface casing is configured to accept the BOP and/or well head equipment, significant hot work is typically required to install BOP flanges or wellhead equipment to the surface casing.